All matter consists of particles called atoms. This is a list of the basic characteristics of atoms:

Atoms cannot be divided using chemicals. They do consist of parts, which include protons, neutrons, and electrons, but an atom is a basic chemical building block of matter.
Each electron has a negative electrical charge.
Each proton has a positive electrical charge. The charge of a proton and an electron are equal in magnitude, yet opposite in sign. Electrons and protons are electrically attracted to each other.
Each neutron is electrically neutral. In other words, neutrons do not have a charge and are not electrically attracted to either electrons or protons.
Protons and neutrons are about the same size as each other and are much larger than electrons. The mass of a proton is essentially the same as that of a neutron. The mass of a proton is 1840 times greater than the mass of an electron.
The nucleus of an atom contains protons and neutrons. The nucleus carries a positive electrical charge.
Electrons move around outside the nucleus.
Almost all of the mass of an atom is in its nucleus; almost all of the volume of an atom is occupied by electrons.
The number of protons (also known as its atomic number) determines the element. Varying the number of neutrons results in isotopes. Varying the number of electrons results in ions. Isotopes and ions of an atom with a constant number of protons are all variations of a single element.
The particles within an atom are bound together by powerful forces. In general, electrons are easier to add or remove from an atom than a proton or neutron. Chemical reactions largely involve atoms or groups of atoms and the interactions between their electrons.

Helpful Things on Atoms:

Atoms's Explanation
Bohr's Model
Bohr's Model Animation
Atoms Overview

Click to Run

Drawing an Atom Bohr Style
Drawing an Atom Bohr Style 2

Helpful Things On the Periodic Table:

Periodic Table Elements Song

Periodic Table Overview

Interactive Periodic Table
Interactive Periodic Table 2
Properties of Elements

Understanding Water:

H20 Video

Electronegativity:

Ionization:

Games and Practice:
Atoms Practice
How Many Protons, Neutrons and Electrons?
Choose the Element
Matching Chemical Symbols with Their Elements
Atomic Structure Jeopardy
40 Element Symbols
Chemical Bonds Mini Quiz
Rags to Riches - Mixtures, Elements and Compounds
Chemical Elements and Their Symbols
Element Hangman
Periodic Table Trivia
Atoms Who Wants to Be a Millionaire
Chemistry Battleship